Exploring New Advances In Internal Fixation

By Gerard V. Yu, DPM, Theresa L. Schinke, DPM, Amanda Meszaros, DPM, and Naohiro Shibuya, DPM

Prior to the broad adoption of the principles and techniques of the AO/ASIF group, cerclage wires, K-wires and Steinmann pins as well as a variety of staples were the more common internal fixation devices employed for stabilizing fractures, osteotomies and fusions. Rigid internal compression fixation techniques eventually became more commonplace and the application of these techniques to foot and ankle surgery has led to clinical advances with improved surgical outcomes. As technology advances and we increase our knowledge of bone healing from a variety of perspectives, newer designs in internal fixation devices have emerged. Some of the more recently designed fixation devices show particular promise in the field of foot and ankle surgery. With this in mind, we take a closer look at emerging two-component compression screws, locking plates and compression staples. How The New Screws Facilitate Better Compression A new generation of compression screws has arrived. These screws are two component devices that allow one to advance the head of the screw independently down the shaft of the screw to obtain additional compression. These screw designs are cannulated to facilitate placement and insertion. If they desire, surgeons may completely bury the head of the screw in bone after they have inserted the device. Examples of these devices include the Kompressor screw (KMI), the I.CO.S Ideal Compression Screw (Integra Lifesciences Corp.) and the Charlotte High Demand Compression Screw (Wright Medical Technology). We have had significant experience with both the Kompressor and the I.CO.S screws. The I.CO.S screw and the newly released Charlotte screw are designed to provide both static and dynamic compression at the osteotomy, fracture or arthrodesis interfaces. The pitch of the head of the screw is smaller than the leading threads at the distal end of the screw, resulting in static compression across the interfaces when the screw is inserted with the standard technique. The mating pitch on the shaft of the screw is actually the same as the leading threads. When the head of the screw is advanced over the shaft, one can then achieve additional dynamic compression. The basic design of the Kompressor device is similar to that of the I.CO.S and Charlotte screws. However, it is not designed to provide static compression. The pitch of the threaded portion of the trailing head of the screw is identical to the pitch of the leading threads. When the screw is inserted into the bone, no compression at the interface occurs other than what one has previously imparted to the site with a mechanical device. In this instance, one can still achieve stability and rigidity of the interface but there will be no compression. The mating thread is actually a “triple lead” thread with a much smaller pitch. This allows each complete revolution of the head of the screw a much faster advancement on the shaft than within the bone, resulting in a significant increase in compression across the interface site. Originally designed for scaphoid fractures of the hand, the Kompressor screw has many applications in foot and ankle surgery including a variety of osteotomies and tarsal bone fractures, including navicular fractures and fifth metatarsal base fractures. The screws are manufactured in two different sizes, a Mini (2.8 mm) and Standard (4.0 mm). The I.CO.S screws are available in 4.0 mm and 6.5 mm sizes. Our experience has been limited to the larger I.CO.S screw, which appears to be ideally suited for major rearfoot fusions such as the subtalar and talonavicular joints as well as calcaneal osteotomies. The technique of inserting the screw is more involved than inserting traditional cannulated and non-cannulated screws. Accordingly, there is a slightly higher learning curve and an increased demand for precise techniques. A more detailed understanding and knowledge of the anatomy of the screw, its mechanism of action and instrumentation are necessary to ensure minimal intraoperative or postoperative complications. The newer compression screws offer advantages that include minimal to no screw head prominence and less screw loosening because the entire screw (head and body) is embedded in bone within the near and far cortices. Limited in vivo testing suggests the I.CO.S screw provides better compression than traditional large cancellous bone screws.

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